Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), flash memory, and resistance variable memory, such as phase change random access memory (PCRAM) and resistive random access memory (RRAM), among others.
The phase change material of a PCRAM device may exist in an amorphous, higher resistance state, or a crystalline, lower resistance state. The resistance state of the PCRAM cell may be altered by applying sources of energy to the cell, such as current pulses or pulses of light, among other sources of energy. For example, the resistance state of the PCRAM cell may be altered by heating the cell with a programming current. This results in the PCRAM cell being programmed to a particular resistance state, which can correspond to a data state. PCRAM devices may also be configured to provide multi-level storage. That is, the memory device may have a plurality of discrete and identifiable states which allow for multi-bit storage in a single memory cell.
Among various phase change materials used for memory devices, one common type includes a phase change chalcogenide alloy such as a Germanium-Antimony-Tellurium (GST) material. The solid phases of GST can rapidly change from crystalline state to amorphous state or vise versa upon heating and cooling cycles. The amorphous GST has relatively higher electrical resistance while the crystalline GST has relatively lower electrical resistance.
One challenge in designing PCRAM cells is that some processing steps, such as chemical mechanical polishing (CMP), etching, and wet clean, among other processing steps, can modify the GST materials. These modifications can cause damage to the GST materials, such as oxidation, phase segregation, and composition shifts, among other damaging effects. Such damage can cause the GST material to not perform as desired when an electrode is in contact with modified GST material.